title: The effect of cyanuric acid on the disinfection rate of Cryptosporidium parvum in 20-ppm free chlorine.
abstract: Cyanuric acid is used to stabilize free chlorine to reduce photodegradation in outdoor swimming pools. While there have been numerous studies examining its effect on the disinfection rates of bacteria and viruses, it is not known whether cyanuric acid can significantly impact the effectiveness of hyperchlorination for inactivating Cryptosporidium oocysts present in fecally-contaminated swimming pools. This study examined the effect of cyanuric acid on the disinfection rate of Cryptosporidium parvum under swimming pool hyperchlorination conditions (20 mg/ml free chlorine). When 50 mg/L cyanuric acid was present there was a 0.70-log10 reduction in oocyst viability after 10 hours as compared to a 3.7-log10 reduction without cyanuric acid. Aids to remediation, such as decreasing the pH to enhance the germicidal efficiency of the free chlorine and doubling the amount of free chlorine residual, were still unable to achieve a 3-log10 reduction. Current public health recommendations for hyperchlorination and pool remediation are insufficient for pools using cyanurate-stabilized chlorine to achieve a three log inactivation of the parasite.
authors.affiliation: Centers for Disease Control and Prevention, National Center for Zoonotic, Vector-borne, and Enteric Disease, Division of Parasitic Diseases, 4770 Buford Highway, Mail Stop F-36, Atlanta, GA 30341-3724, USA. jshields1@cdc.gov
authors.forename: Joan M
authors.initials: JM
authors.lastname: Shields
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Arrowood
authors.forename: Vincent R
authors.initials: VR
authors.lastname: Hill
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Beach
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002713:Chlorine; D015169:Colony Count, Microbial; D016785:Cryptosporidium parvum / Q000187:drug effects* / Q000302:isolation & purification; D004203:Disinfection; D004285:Dogs; D005243:Feces / Q000469:parasitology; D006863:Hydrogen-Ion Concentration; D033661:Oocysts; D012973:Sodium Hypochlorite; D013551:Swimming Pools; D014227:Triazines / Q000494:pharmacology*; D018508:Water Purification / Q000379:methods*
chemical_list: D014227:Triazines; D002713:Chlorine; D012973:Sodium Hypochlorite; C004632:cyanuric acid